A lithium secondary battery is an energy storage device in which electrical energy is stored in the battery while lithium moves from an anode to a cathode during a discharge process and lithium ions move from the cathode to the anode during charging. When compared to other batteries, lithium secondary batteries have higher energy density and lower self-discharge rate, and thus, the lithium secondary batteries have been widely used in various industries.
Components of a lithium secondary battery may be classified as a cathode, an anode, an electrolyte, and a separator. Lithium metal was used as an anode active material in an early lithium secondary battery. However, since safety concerns may occur as charge and discharge are repeated, lithium metal has been replaced with a carbon-based material, such as graphite. Since a carbon-based anode active material may have an electrochemical reaction potential with lithium ions that is similar to lithium metal and changes in a crystal structure may be small during continuous intercalation and deintercalation processes of lithium ions, continuous charge and discharge may be possible. Therefore, excellent charge and discharge lifetime may be provided.
However, techniques for developing a high capacity and high power anode active material have been required as the lithium secondary battery market has recently expanded from small-sized lithium secondary batteries used in portable devices to large-sized secondary batteries used in vehicles. Therefore, development of non-carbon-based anode active materials based on materials, such as silicon, tin, germanium, zinc, and lead, having a higher theoretical capacity than a carbon-based anode active material has been conducted.
The above anode active materials may increase energy density by improving charge and discharge capacity. However, since dendrites or a non-conductive compound may be generated on an electrode as the charge and discharge are repeated, charge and discharge characteristics may degrade or expansion and shrinkage may increase during the intercalation and deintercalation of lithium ions. Therefore, with respect to secondary batteries using the above anode active materials, retention of discharge capacity (hereinafter, referred to as “lifetime characteristics”) according to the repeated charge and discharge may be insufficient, and a ratio of initial discharge capacity to initial charge capacity after manufacturing (discharge capacity/charge capacity; hereinafter, referred to as “initial efficiency”) may also be insufficient.